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Mesopelagic fishes dominate otolith record of past two millennia in the Santa Barbara Basin.

ABSTRACT: The mesopelagic (200-1000?m) separates the productive upper ocean from the deep ocean, yet little is known of its long-term dynamics despite recent research that suggests fishes of this zone likely dominate global fish biomass and contribute to the downward flux of carbon. Here we show that mesopelagic fishes dominate the otolith (ear bone) record in anoxic sediment layers of the Santa Barbara Basin over the past two millennia. Among these mesopelagic fishes, otoliths from families Bathylagidae (deep-sea smelts) and Myctophidae (lanternfish) are most abundant. Otolith deposition rate fluctuates at decadal to centennial time scales and covaries with proxies for upper ocean temperature, consistent with climate forcing. Moreover, otolith deposition rate and proxies for temperature and primary productivity show contemporaneous discontinuities during the Medieval Climate Anomaly and Little Ice Age. Mesopelagic fishes may serve as proxies for future climatic influence at those depths including effects on the carbon cycle.

SUBMITTER: Jones WA

PROVIDER: S-EPMC6783546 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Mesopelagic fishes dominate otolith record of past two millennia in the Santa Barbara Basin.

Jones William A WA Checkley David M DM

Nature communications 20191008 1

The mesopelagic (200-1000 m) separates the productive upper ocean from the deep ocean, yet little is known of its long-term dynamics despite recent research that suggests fishes of this zone likely dominate global fish biomass and contribute to the downward flux of carbon. Here we show that mesopelagic fishes dominate the otolith (ear bone) record in anoxic sediment layers of the Santa Barbara Basin over the past two millennia. Among these mesopelagic fishes, otoliths from families Bathylagidae ...[more]

PMID: 31594950

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Project description:DNA barcode sequences were developed from 557 mesopelagic and upper bathypelagic teleost specimens collected in waters off Atlantic Canada. Confident morphological identifications were available for 366 specimens, of 118 species and 93 genera, which yielded 328 haplotypes. Five of the species were novel to the Barcode of Life Database (BOLD). Most of the 118 species conformed to expectations of monophyly and the presence of a "barcode gap", though some known weaknesses in existing taxonomy were confirmed and a deficiency in published keys was revealed. Of the specimens for which no firm morphological identification was available, 156 were successfully identified to species, and a further 11 to genus, using their barcode sequences and a combination of distance- and character-based methods. The remaining 24 specimens were from species for which no reference barcode is yet available or else ones confused by apparent misidentification of publicly available sequences in BOLD. Addition of the new sequences to those previously in BOLD contributed support to recent taxonomic revisions of Chiasmodon and Poromitra, while it also revealed 18 cases of potential cryptic speciation. Most of the latter appear to result from genetic divergence among populations in different ocean basins, while the general lack of strong horizontal environmental gradients within the deep sea has allowed morphology to be conserved. Other examples of divergence appear to distinguish individuals living under the sub-tropical gyre of the North Atlantic from those under that ocean's sub-polar gyre. In contrast, the available sequences for two myctophid species, Benthosema glaciale and Notoscopelus elongatus, showed genetic structuring on finer geographic scales. The observed structure was not consistent with recent suggestions that "resident" populations of myctophids can maintain allopatry despite the mixing of ocean waters. Rather, it indicates that the very rapid speciation characteristic of the Myctophidae is both on-going and detectable using barcodes.

Project description:Newly described phylogenetic lineages within the domain Archaea have recently been found to be significant components of marine picoplankton assemblages. To better understand the ecology of these microorganisms, we investigated the relative abundance, distribution, and phylogenetic composition of Archaea in the Santa Barbara Channel. Significant amounts of archaeal rRNA and rDNA (genes coding for rRNA) were detected in all samples analyzed. The relative abundance of archaeal rRNA as measured by quantitative oligonucleotide hybridization experiments was low in surface waters but reached higher values (20 to 30% of prokaryotic rRNA) at depths below 100 m. Probes were developed for the two major groups of marine Archaea detected. rRNA originating from the euryarchaeal group (group II) was most abundant in surface waters, whereas rRNA from the crenarchaeal group (group I) dominated at depth. Clone libraries of PCR-amplified archaeal rRNA genes were constructed with samples from 0 and 200 m deep. Screening of libraries by hybridization with specific oligonucleotide probes, as well as subsequent sequencing of the cloned genes, indicated that virtually all archaeal rDNA clones recovered belonged to one of the two groups. The recovery of cloned rDNA sequence types in depth profiles exhibited the same trends as were observed in quantitative rRNA hybridization experiments. One representative of each of 18 distinct restriction fragment length polymorphism types was partially sequenced. Recovered sequences spanned most of the previously reported phylogenetic diversity detected in planktonic crenarchaeal and euryarchaeal groups. Several rDNA sequences appeared to be harbored in archaeal types which are widely distributed in marine coastal waters. In total, data suggest that marine planktonic crenarchaea and euryarchaea of temperate coastal habitats thrive in different zones of the water column. The relative rRNA abundance of the crenarchaeal group suggests that its members constitute a significant fraction of the prokaryotic biomass in subsurface coastal waters.

Dataset Information

Mesopelagic fishes dominate otolith record of past two millennia in the Santa Barbara Basin.

Publications

Mesopelagic fishes dominate otolith record of past two millennia in the Santa Barbara Basin.

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